Resins

Resins are obtained from numerous species of coniferous and deciduous trees by oxidation or polymerization of the volatile oils of these trees. They are heterogeneous bodies both chemically and physically. In their natural state, they are hard substances. They occur in the form of lumps of various shapes, sizes and colors, and varying degrees of transparency.
Resins are insoluble in water, but dissolve in volatile oils, in drying oils and in various organic solvents.
Resins in the solid state usually have an amorphous structure and do not volatilize at normal temperatures. At higher temperatures, they melt.
Depending on the degree of hardness, resins are divided into:

• hard,
• soft,
• medium-hard.

Among the most durable are amber and copal.

Copal

They come from tropical countries (India, Africa, South America and Australia). They belong to the acid resins.

Zanzibar copal (East Africa)

In terms of hardness, it is second only to amber. Melting point: 160 ÷ 360°C. It has the shape of flat nuggets with a yellow color and a characteristic rough surface (so-called "goosebumps").
In the breakthrough glassy, weakly colored.
Dissolves partially in spirit, acetone, ether, chloroform and benzene, as well as in rosemary oil (softening effect).

Mozambique

Madagascar (East African) copal. Similar to Zanzibar in terms of persistence.

Kauri

It has many varieties. It is harvested in huge quantities in New Zealand in the form of lumps.
Its melting point is 120 ÷ 180 ° C. It is soluble in amyl alcohol and in a mixture of spirit and acetone.
In chloroform, acetone, toluene it partially dissolves.

Manilla

Occurs in more than 50 varieties dissolved in combined solvents such as spirit with turpentine, acetone with turpentine.
All varieties are soluble in acetone. The melting point is 112 ÷ 190°C.
African copal is the most durable. Asian ones are of medium hardness, Australian ones are the softest.

Amber

A resin found in earth deposits. The main deposits are located on the shores of the Baltic Sea.
Color from light yellow to dark brown, transparent or milky opaque.
The noble species, the so-called "suecynite," comes from Pinus suecinifera trees. It is the hardest natural resin known since ancient times and extremely difficult to dissolve.
It melts at 365 ÷ 380°C.
In spirit it dissolves up to 30%, in ether up to 20%, in chloroform 25%.
Small amounts of amber can be dissolved at high temperatures in oil into a boiled oil varnish, very dark (almost black).
By dry distillation of amber at 400°C, it transforms into amber rosin, which is soluble in warm oils.
Attempts to dissolve amber directly have been only partially successful.
Amber varnishes are not suitable for varnishing the surface of paintings, as they yellow, lose their transparency over time and are difficult to remove (hard).
When cold, amber does not dissolve.
Unlike copal, which mainly consists of resin acids, the most important components of amber are complex esters containing spirits and resin acids.
All copal and amber are subjected to dry distillation, and only then dissolved in hot oil or other solvents.